Post-tensioned prestressed concrete members



Jan. 31, 1967 K. H. MIDDENDORF 3,300,921

POST-TENSIONED PRESTRESSED CONCRETE MEMBERS Filed Nov. 15, 1961 e Sheets-Sheet 1 IN VEN TOR. KARL H. M/DDENDORF BY RM A T TORNEY 1967 K. H. MIDDENDORF 3,300,921

POST-TENSIONED PRESTRESSED CONCRETE MEMBERS Filed Nov. 13, 1961 s Sheets-Sheet 2 IN VEN TOR. KARL H. M/DDENDORF AT TORNE Y Jan. 31, 1967 K. H. MlDDENDbRF 3,300,921

POST-TENSIONED PRESTRESSED CONCRETE MEMBERS Filed Nov. 13, 1961 esheets-sneei 4? 3 M32 a I 7/ 44 54 Fig.6

32 73 'r/ 47 ,M 4 .;7 6 Y4" 34 35 I -74- v 47 Fig. 9 30 30 3o 65 66 I I 30 37 32 1 1 1 I t A 38 l I 38 4 66 1 4 36 3 g 1 39 9. as. L 5/ F o INVENTOR. 34 49 54 49 34 4 5 KARL H. woos/wom- 44 46 A T TOPNE Y Jan. 31, 1967 K. H. MIDDENDORF 3,300,921

POST-TENSIONED PRESTRESSED CONCRETE MEMBERS Filed Nov. 13, 1961 6 Sheets-Sheet 4 INVENTOR. KARL H. M/DDENDORF A T TORNEY Jan. 31, 1967 I K. H. MIDDENDORF POSTTENSIONED PRESTRESSED CONCRETE MEMBERS Filed Nov. 15, 1961 6 Sheets-Sheet 5 IN VEN TOR. KA PL H. M/DDEND ORF A TTORNEY Jan. 31, 1967 K. H. MlDDENDORFf 3,300,921

POST-TENSIONED PRESTRESSED CONCRETE MEMBERS Filed Nov. 13, 1961 6 Sheets- Sheet 6 INVENTOR. 101 PL H. MIDDENDORF A TTOR/VE Y Fig. 23

United States Patent 3,300,921 POST-TENSIGNED PRESTRESSED CONCRETE MEMBERS Karl H. Middendorf, Costa Mesa, Califi, assignor to The Prescon Corporation, a corporation of Texas Filed Nov. 13, 1961, Ser. No. 151,633 7 Claims. (Cl. 52-227) My invention relates to an apparatus for post-tensioning concrete prestressing members that are in the form of fiat tendons and the method of post-tensioning such prestressing members. This application is a continuation in part of my applications Serial No. 3,851, filed January 21, 1960, on Method and Apparatus for Post-Tensioning Concrete Prestressing Members, now abandoned, and Serial No. 468,762, filed November 15, 1954, on Post-Tensioning Method and Apparatus for Prestressing Members, now Patent No. 3,029,490, patented April 17, 1962. A flat tendon comprises a high tensile strength element of varying length that is of greater width than thickness, and usually of considerably greater width than thickness.

Such flat tendons are particularly advantageous in the type of construction called thin shell design, a flat tendon being preferable to a round tendon in such structures because it permits thinner sections with ample coverage of concrete of the metallic tendon to protect it against weather and fire. Similarly, elongated end hardware of a flat pattern permits reduction in thickness of the concrete structure. Such flat tendons are particularly advantageous in a flat slab concrete construction and in concrete structures that follow a parabolic or circular pattern, such as, for instance, a prestressed circular body such as a tank.

It is a particular purpose of my invention to provide a tendon for prestressing reinforced concrete structures that has a flat main body portion comprising a plurality of tension members, such as high tensile strength wires, extending longitudinally of the tendon and clips engaging said tension members at longitudinally spaced intervals to hold said tension members in side by side relationship in a transverse row or in transversely aligned relationship with respect to the length of the tendon. Such a flat tendon has great advantages over rolled flat high strength alloy bars, for example, as the wire tension members are of a higher tensile strength than such a bar for the same cross section, and are not difficult to anchor, as is the case with such bars.

One of the important purposes of my invention is to provide an improved coupling means between tendons mounted in adjacent sections of a long concrete structure.

It is a purpose of my invention to provide a positive anchorage for post-tensioned tension members in prestressed concrete, which is assembled ready for installation in the concrete structure in such a manner that none of the parts thereof can be displaced or lost and which is provided with a connection, between a pulling member of a stressing apparatus, such as a hydraulic jack, and the stressing member of the post-tensioning means, which can be readily made by simple sliding engagement of the pulling member with the stressing member and which requires no screw-threaded or similar machined connections. It is a further purpose of my improved method to provide an anchorage whereby prestressing can be extended by coupling on added tension members where a plurality of slabs are cast in edge to edge relation, and which also is adapted for extending a coupling means across a knit or closure strip between sections of a lift slab structure whereby the prestressing across the structure is continuous, or for other structures in which continuity is desirable.

ice

that slippage of the wires with respect to the concrete will be provided, and as this coating material is preferably placed onrthe tendon before it is shipped to the point of use, a wrapping of suitable material is preferably provided around the coated tendon.

Furthermore the means for holding the wires in side "by side position to form the flat body portion of the movement in all directions relative to each other.

tendon is of such a character that the wires can readily slide therethrough, resiliently gripping the wires so that there is only frictional engagement between the wires and ,the clips that are provided to hold them in their side by side relationship. The preferred clip comprises a pair ofduplicate high strength or heat treated steel retaining members that are of a sufficiently springy character that a pair of said members can be placed in engagement with ,the side by side wires on opposite sides thereof, said mem bers having hook ears thereon extending around the marginal wires of the tendon in opposite directions so that when the pair of spring retaining members forming the clip are place-d in position the wires will be held from However, said retaining members or clips are not made so as to fit the side by side bundle of wires so tightly that said wires can not move through the clips in being pulled to put the tendon under stress.

It is a further specific purpose of my invention to provide a method of securing high tensile strength steel tension members in position to prestress a concrete structure comprising securing together a bearing member,

that has openings therethrough, and a stressing member that also has openings therethrough that align with the openings in the bearing member, by means of a temporary connection, inserting the tension members through the openings with a portion of each thereof projecting from the side of the stressing member remote from the hear ing member, forming an enlargement of sufficient size to prevent passage thereof through said openings on the projecting portions of the tension members, and positioning said enlargements against the stressing member, said temporary connectionproviding suitable means for holding the enlargement in position. All these steps are carried out at an established assembly point prior to placing of the tension means in position in the concrete structure. Then the tension members and the bearing members are placed in position and the concrete poured,

. the bearing member anchored to the concrete structure by the setting of the concrete and after the concrete I away from the bearing member a distance to place the the tension on the tension members.

desired tension on the tension members and spacing means is inserted between the bearing member and the stressing member to hold the stressing member in properly spaced relation from the bearing member to maintain In applying my method to the particular fiat tendon, a plurality of tension members held in their fiat side by side relationship is passed through a row of openings in the bearing plate and in a bar-like stressing member.

My invention further includes the method of prestressing a concrete structure comprising a plurality of adjacent slabs, beams or other sections of concrete structures, in such a manner that the adjacent sections will be pressed tightly into engagement.

Said method involves the provision of yielding means surrounding the .1) coupling member so as to permit sufiicient movement of the coupling member relative to the concrete of the second slab that said coupling member will not interfere with the action of the second slab in pressing edgewise against the first slab.

Other objects and advantages of my invention will appear as the description of the drawings proceeds. I desire to have it understood, however, that I do not intend to limit myself to the particular details shown or described, except as defined in the claims.

In the drawings:

FIG. 1 is a plan view of the end portions of one of my improved tendons, a fragmentary portion of the mid-portion or main body portion thereof being shown.

FIG. 2 is a similar view of a modified form of tendon.

FIG. 3 is a similar view of a further modified form of tendon.

FIG. 4 is a section taken on the line 4-4 of FIG. 1 on an enlarged scale.

FIG. 5 is a section taken on the line 5-5 of either FIG. 1 or FIG. '2 on an enlarged scale.

FIG. 6 is an end elevation taken On the line 6-6 of FIG. 2 on an enlarged scale.

FIG. 7 is a section taken on the line 7-7 of FIG. 2 on an enlarged scale.

FIG. 8 is a section taken on the line 8-8 of FIG. 3 on an enlarged scale.

FIG. 9 is a section taken on the line 9-9 of FIG. 3 on an enlarged scale.

FIG. 10 is a section taken on the line 10-10 of FIG. 1 on an enlarged scale.

FIG. 11 is a section taken on the line 11-11 of FIG. 10.

FIG. 12 is a top plan view taken on the line 12-12 of FIG. 10.

FIG. 13 is a section taken on the line 13-13 of FIG. 5.

FIG. 14 is a view partly in section and partly in elevation through a fragmentary end portion of a concrete slab and tendon provided with a stressing bar and showing a fragmentary portion of pulling means for stressing the tendon. i

FIG. 15 is a vertical sectional view through portions 3 of a concrete slab to which my invention is applied, partly broken away.

FIG. 16 is a similar view of another concrete slab showing a different tendon therein than in FIG. 15.

FIG. 17 is a view similar to FIG. 14 showing the position of the stressing bar after the tendon has been stressed and the pulling means removed.

FIG. 18 is a section taken on the line 18-18 of FIG. 17.

FIG. 19 is a view partly in elevation and partly in section of the fragmentary end portion of a concrete slab showing a dead end anchoring means for the tendon.

FIG. 20 is a transverse sectional view through a resilient clip member and the wires of the tendon held in side by side relation thereby after assembly in the con crete structure, showing a fragmentary portion of the surrounding concrete structure.

FIG. 21 is a fragmentary enlarged vertical sectional view through the marginal edge portions of adjoining slabs and the tendons associated therewith.

FIG. 22 is a horizontal sectional view through a cylindrical concrete structure showing my invention applied thereto, and

FIG. 23 is a section taken on the line 23-23 of FIG. 22 on an enlarged scale.

Referring in detail to the drawings, in FIG. 1 is shown a tendon that is made up of a plurality of tension members 30 that are in the form of high tensile strength wires. Said tension members are held in side by side relationship, preferably in close adjacency to each other throughout the main body portion of the tendon, the major portion of which is broken away in FIG. 1, by means of spring clips or clamping members 31, which are located at regularly spaced intervals through out the major portion of the length of the tendon. In the form of the invention shown in FIG. 1 a bearing member in the form of a plate 32 is provided at each end of the tendon and a stressing member in the form of a bar 33 is also provided at each end thereof. The wire tension members 30 are each provided with a head 34 at each end thereof, the tension members 30 extending through suitable openings in the bearing plates 32 and stressing bars 33, said heads 34 being of such a size as to not pass through the openings in the stressing bars and bearing plates.

It is desirable that means be provided for holding the heads of the wires, the stressing bars and the bearing plates in proper position with respect to each other, for mounting in the form, for the bearing plate to be embedded in the concrete and the headed wires and stressing members accessible for engagement with suitable pulling means to put the tendon under stress. The holding means preferably comprises a channel-shaped in cross section retainer bar 35 and headed screw-threaded fastening elements 36, the heads of which engage the retaining bar 35 and the screw-threaded shanks of which are screw threadedly engaged with screw-threaded openings in the bearing plate 32.

In FIGS. 4, 5 and 13 the end structure of the tendon shown in FIG. 1 is shown more in detail. The bearing plate 32 is elongated transversely of the length of the tendon, is provided with a row of openings 37 therein that are of a size such that the wire tension members 30 will be slidable therethrough and with a pair of internally screw-threaded openings 38 at opposite ends thereof, with which the screw-threaded headed members 36 screwthreadedly engage. The stressing bar 33 is provided with a longitudinal row of openings 39, through which the wires 30 slidably extend, said openings being of such a size that the heads 34 on the wires can not pass therethrough. Said stressing member or stressing bar 33 is provided with a fiat face 40 that engages flatly face to face with the fiat outer face of the bearing member or bearing plate 32 and has parallel side walls 41 that extend perpendicularly to the face 40 and an enlarged head portion 42, which has a transversely curved periphery 43 and a central indentation 44 running lengthwise thereof for seating the heads 34 of the wires 30 thereagainst. An inclined undercut shoulder 45 is provided running longitudinally of the stressing bar 33 on each side thereof at the junction of the head portion 42 with the portion of the stressing bar having the parallel side walls 41.

The channel-shaped in cross section retainer member 35 is made of steel and is provided with a transverse portion 46 and a pair of legs 47 extending perpendicularly to the transverse portion 46 and connected therewith by curved portions 48. The heads 34 have flat portions 49 on their sides remote from the junction of said heads with the main body portion of each of the Wires 30, the flat faces 49 engaging with the inner sides of the transverse portions 46 of the retainer members. Mounted between the heads 50 of the screw-threaded headed fastening elements 36 and the outer side of the transverse portion 46 of the retainer member 35 are washers 51, which may be of fiber or steel. The retaining means comprising the channel-shaped retainer bars 35 and the headed fastening elements 36 are thus detachably connected with the bearing plate 32 and are re-usable a large number of times. With the parts in the position shown in FIGS. 1, 4, 5 and 13 the end anchoring structure comprising the bearing plates 32, the stressing bars 33 and the heads 34 on the wire members 30 is held in proper assembled relation so that the bearing plates 32 and the body portions of the tendon can be mounted in the form for the concrete structure in which the tendon is to be used so that the bearing plate 32 will be embedded in the concrete after pouring the same. The retainer members 35 are femoved before the concrete is poured and the stressing bars 33 will be in an accessible position after the concrete is poured and set for attachment of a suitable pulling member to the stressing bar for moving the same the required distance away from the bearing plate to put the wire tension members 30 under the desired tensile stress. Suitable spacing means are then put between the stressing bar 33 and the bearing plate to maintain the stressing bar 33 in the proper position for maintaining the stress on the headed wires 30. l i

A fragmentary portion of such pulling means is shown in FIG. 14, the pulling member being indicated generally by the numeral 52, which is provided with a pair of jaws 53 that are mounted toswing about the pivot members 54 and which have forwardly extending legs 55 terminating in inturned end portions 56 that have undercut shoulders 57 thereon engaging with the undercut shouders 45 provided on the stressing bar 33. The'action of the undercut shoulders 45 and 57 is such that the greater the force exerted by the pulling memberon the stressing member 33 the greater the force urging the jaws 53 toward each other in firm engagement with the head portion of the stressing member 33, thus forming interlocking means connecting the pulling members with the stressing member 33.

The pulling member 52 moves the stressing bar 33 outwardly away from the bearing plate 32 until the wires 30 are put under the desired tension, which is determined by means of a suitable gauge. This is done after the concrete body 58, in which the bearing plate 32 has been mounted, has set sufficiently for the stressing of the ten sion members 30 to take place. In FIG. 17 the stressing bar 33 is shown in the position that it has after the pulling means has been disengaged therefrom and the parts are in the position which they have for prestressing the concrete structure. In order to maintain the stressing bar 33 in its spaced relationship to the bearing plate 32,

spacing members or shims 59 are placed in position between the stressing bar 33 and the bearing plate 32-. Said shims 59 and the bearing plate 32 are preferably made of steel, the type of steel preferably used being commonly known as plow steel. Said shims are preferably made of a rectangular character, having flat end faces 60, flat sides 61 extending perpendicularly to the end faces 60 and fiat sides 62 extending perpendicularly to the flat sides 61 and the end faces 60. Flat end faces 60 thus engage flatly with the fiat outer faces of the bearing plates 32 and the flat faces 40 of the stressing bars 33. My improved tendon can be made up with any number of wire tension members that may be desired to produce the desired tendon having the desired transverse width. The number of wires shown in the drawings is merely illustrative. If an even number of wires is used, the arrangement of shims 59 would be similar to that shown in FIGS. 17 and 18, but if one less wire were embodied in the tendon the same number of shims would be required as are shown in FIG. l8, as there must be a wire on each side of each of the shims 59 to retain the parts in position in the finished structure.

The spring clips 31 are also mounted on the tendon at the place of assembly before shipping to the place of use. Each of said clips 31 comprises a pair of resilient members, said resilient members being indicated by the numerals 63 and 64 in FIGS. l0, l1, l2 and 20. The resilient members 63 and 64 are made of spring metal and are tempered so as to maintain their shape, or are made of high strength steel, but being of sutlicient springiness that the same can be readily placed in position around the wires 30 at regularly spaced intervals along the length thereof. When so placed said paired members 63 and 64 constitute resilient clamping means frictionally engaging the Wires 30. Said members 63 and 64 are placed in side by side relationship lengthwise of the wires 3b, as shown in FIGS. 11 and 12. Each of said resilient'memhere 63 and 64 making up the resilient clamping means G. has a straight body portion, said body portions'flatly engaging the opposite sides of the group of wires 30, as will be obvious from FIG. 10. Each of said resilient members also has a hook end that is made up of a curved portion and an end portion that overlies the marginal wire 30 of the group forming the flat body portion of the tendon. The curved end portions of the resilient member 63 are indicated by the numeral 65 and the end portions forming retaining ears by the numeral 66, while the curved end portions of the other resilient member 64 are indicated by the numeral 67 and the end portions or cars thereon by the numeral 68. It will be obvious that with the paired members 63 and 64 placed in position in close adjacency as shown in FIG. 11, the resilient gripping action of the curved ends 65 and 67 and the ears as and 63in cooperation with the body portions of the members 63 and 64 will resiliently clamp the wires 33 in alignment in a row transversely of the tendon against any substantial movement in any transverse direction. However, due to the resilient character of the members 63 and 6-4, the same only frictionally engage the wires 30 and the wires can slide through the resilient clamping means made up of the parts 63 and 64 when this is necessary due to the pull exerted on the wires 30 in putting the same under tension. Any suitable means may be provided to prevent bonding of the tension members 30 to the concrete body 58. A coating material 69 for this purpose is illustrated as being applied to the surface of the wires 30 and to the retaining clips 31 in FIG. 20, which shows a fragmentary cross sectional portion of a concrete body 58, in which the tendon is mounted. In order to retain the coating material undisturbed on the wire members 3%) and clips 31 after assembly thereof at the place of manufacture and during transportation thereof and placing thereof in the form, a suitable outer Wrapping, is wrapped around the coated tendon, being indicated by the numeral 70 in FIG. 20.

The stressing member 33 is made of an aluminum alloy and is extruded in the form of a bar of indefinite length of the cross section of the stressing member as viewed in FIGS. 5, 14 and 17, said stressing member being cut off of desired length for the length stressing bar to be utilized as the stressing member in a particular tendon, and holes drilled therein for the wires 30.

Referring to FIG. 3, a tendon is shown that has the same number of wires 30 provided therein as in the tendon shown in FIG. 1, and said wire tension members 30 are provided with resilient clamping members or spring clips 31 for holding the same in side by side adjacency transversely of the tendon in the same manner as previously described. However, instead of providing a stressing member at each end of the tendon, a bearing plate 32, a stressing member 33, and a retaining member 35, se cured by means of the bolts 36 to hold the heads 34 on the wires and the bearing plate 32 and stressing member 33 in proper relative relationship for positioning the tendon in a concrete form, is only provided at the right hand end of the tendon shown in FIG. 3.

The left hand end of the tendon is provided with a dead end anchor. Said dead end anchorage comprises a bearing plate 32 and an anchor bar 71 having openings 72 therein aligning with the openings 37 in the anchor plate 32, said bar being rectangular in cross section so as to have flat side faces thereon and fiat ends, the openings 37 and 72 being of such diameter that the heads 34 of the wires 30 will not pass therethrough. A retainer member 35' is provided for holding the heads 34 on the wires, the bar 71 and the anchor plate 32 in assembled relationship, so as to keep these parts in their proper position during transportation from the place of manufacture to the place of use of the tendon. Said retainer 35' is made in the same manner as the retainer 35 previously described, except that it does not have any holes therein for the headed fastening elements 36, such as used with the retaining member 35. The same reference numerals I are applied to the various parts of the retainer member 35' as were applied to the corresponding parts in connection with the retainer member 35.

The legs 47 of said retainer member 35' are welded to the narrow side faces of the rectangular in cross section bar 71, as at 73, and said bar 71 is welded at the marginal edges thereof to the bearing plate 32 by the welds 74. Thus the retainer member 35 is rigidly secured to the bearing plate 32 and holds the heads 34 of the wires in fixed position with respect to the bearing member 32. Similarly, the bar 71 is held in fixed position with respect to the bearing plate 32, the welds not being disturbed in the use of the tendon, as the tendon is pulled entirely from one end thereof, the parts of the dead end anchorage remaining in the relative position that they have after having been assembled and welded, after having been placed in position in the form and the concrete poured around the wires and the bearing member. As illustrated in FIG. 19, the dead end anchor is shown as being mounted along one marginal edge portion of a concrete body 58', but may be embedded in the concrete to protect it from fire and weather.

Referring now to FIG. 16, the concrete body 58' is shown as being a slab that has the end portions 75 mounted on suitable supporting structure 76 cast integral with the slab 58, and which is provided with a beam 77 cast integral with the slab 58' midway between the end margins 75 thereof. A tendon 78, which is constructed in the manner illustrated in FIG. 3, is shown extending lengthwise of the slab and other tendons 79 and 81) are shown extending transversely of the slab. The tendon 78 is mounted in the slab 58' so as to gradually slope downwardly from the ends thereof to the place of nearest approach to the bottom face 81 of the slab midway between the supporting means and approaches nearest to the top surface 82 of the slab where the slab is supported by the supporting means 76 and 77. The transversely extending tendons 79 and 80 are similarly located, as will be obvious from FIG. 16. It will also be obvious that with a fiat tendon, such as the applicant provides, the individual tension members can be collectively located much more closely to the lower and upper faces 81 and 82 of the concrete slab structure 58' than if these were arranged in a circular pattern, and still leave enough concrete between the metal tension members of the tendon and the outer faces of the concrete structure to protect the same against fire and other hazards.

In FIG. 2 the tendon is provided with the anchoring means that includes the stressing member at the left hand end thereof, said anchorage comprising the bearing plate 32, the stressing bar 33, the heads 34 on the high tensile strength wires 30, which are held in side by side adjacency by means of the clips or resilient clamping members 31 in the same manner as described for the tendons shown in FIGS. 1 and 3, these parts being held in the same relation as previously described by means of the headed screwthreaded elements 36 and the retainer member 35. The opposite end of the tendon shown in FIG. 2 is provided with a coupling member 92, but is not provided with any retainer member, as the anchorage is of such a character that the retainer member is not adapted for engagement therewith.

The anchorage provided at the right hand end of the tendon shown in FIG. 2 is shown more in detail in FIGS. 6 and 7, the anchorage comprising a bar 92 that is of a generally U-shaped cross section or channel-shaped in cross section, having a transverse portion 83, which is provided with a row of openings 84 of such a size that the heads 34 of the wire tension members 30 can not pass therethrough. Said bar further has diverging legs 85 that terminate in end portions 86, that are provided with rounded surfaces 87, and which have inwardly extending portions 88 that extend toward each other and Which provide undercut shoulders 89 on said legs 85. A shallow groove 90 may also be provided on the outer side of the transverse portion 83. The legs are joined with the transverse portion 83 by means of curved surfaces 91 on the inner face thereof, providing a seat for the heads 34 of the wires 30 on the inner face of the transverse portion 83. The channel-shaped bar 92 is made of aluminum alloy similar to that used for the stressing bar 33 and is extruded in the form of a bar of indefinite length having the cross sectional shape down in FIG. 7 and cut otf to desired length for use as a coupling member in a manner to be described below.

The coupling member 92 is shown in position in a slab 93, which is a section of a concrete structure that includes the slab 94, the slab 94 being mounted on suitable supporting members 95 and 96 cast integral therewith and the slab 93 being provided with supporting means 97 cast integral therewith. The tendon 78 provided in the slab 94 is provided with the anchoring means including a stressing member in the form of a bar 33 at opposite ends thereof as shown in FIG. 1, the stressing members being shown at 33 at both ends of the tendon 78' in FIG. 15 in spaced relationship to the bearing plates 32 and with spacing members 59 between the bearing plates and the stressing members 33, the tendon 80' being positioned in a similar manner to that shown in FIG. 16. The coupling member 92 is connected with the stressing member 33 at the joint 98 between the slabs 93 and 94, the tendon shown in the slab 93 being designated by the reference numeral 78" and the transverse tendon shown diagrammatically therein is indicated by the numeral 80". In FIG. 15 the left hand end of the tendon 78 is shown as being provided with a bearing plate 32, a stressing member 33 and spacing members 59, the heads 34 of the tendons 78 and 78" at the opposite marginal portions of the slabs 93 and 94 being shown as being in engagement with the stressing members 33 and with the coupling member 92.

Referring now to FIG. 21, in which the joint between the slab sections 93 and 94 is shown more in detail, the wire tension members 30 are shown as extending through the openings 37 in the bearing plate 32 and as having the heads 34 thereon in engagement with the stressing member 33 and with the spacing members 59 in position between the bearing plate and the stressing member 33. The position of the parts is that in which the high tensile strength wire tension members 30 are in stressed conditron.

The coupling member 92 is engaged with the stressing member 33 by sliding the same longitudinally of the stress ing member with the inward extensions 88 thereof back of the head portion 42 of the stressing member 33 and with the undercut shoulders 89 thereof in engagement with the undercut shoulders 45 of the stressing bar 33, said undercut shoulders comprising interlocking means connecting said coupling member 92 and stressing member 33. It will be obvious that with the use of the undercut shoulders 89 and 45 on the members 92 and 33, if a pull is exerted on the tendon 78" to the left in FIG. 21, the high tensile strength wire tension members 30, through the heads 34 thereon, will pull the coupling member 92 and thus the stressing member 33 toward the left and the greater the pull exerted on the members 30 and thus on the coupling member 92 the more firmly the undercut shoulder portions 45 and 89 will engage, and any force tending to flex the legs 85 will tend to flex them toward each other to more firmly couple the members 33 and 92. After the coupling member 92 has been engaged with the stressing member 33 by such longitudinal sliding of the same into interlocked position therewith, a yieldable sheath 99 is put in position on the peripheral surface of the coupling member 92, following the outer contour thereof and having inwardly curved end portions 100 and 101 extending around the end portions of the coupling member to prevent disengagement of the sheath from the coupling member. Said yieldable sheath is preferably made of sponge rubber or similar compressible material.

The purpose of the structure shown in FIGS. and 21 is to provide means whereby the marginal portion of the slab 93 at the joint 98 will be pressed tightly into engagement with the marginal portion of the slab 94. In constructing the sections of the slab shown in FIG. 15 the tendon 78 is put in position in the form and, presuming that the slab 94 is of such great length that the tendon 78' has tobe pulled from both ends, after the concrete has set, the tendon is stressed by pulling on the stressing members 33 and inserting the spacing members 59 after said stressing members have reached the position desired therefor to put the desired stress on the tendon 7 3.

After the slab 94 has set sufficiently for carrying out this stressing action and the parts of the tendon 78 are in the position shown in FIGS. 15 and 21, the tendon 73 having the coupling member 92 is connected with the tendon 78' and placed in position in the form for the slab 93, the sheath 99 being placed in position on the coupling member 92 as above described.

After the slab 93 has been poured and has set sufficiently for tensioning the tendon 78", the tendon 70" is stressed by pulling on the stressing bar 33 at the left of FIG. 15, the spacing member 59 put in position and the pulling means uncoupled. Having thus stressed the tension members 30 of the tendon '78", the concrete body of the slab 93 will be put under compression, which will cause the marginal edge thereof engaging the adjacent edge of the concrete body 94 to be pressed tightly thereagainst, thus preventing any openings or cracks between the two adjacent concrete bodies 93 and 94. The slight movement of the anchor member 92 from the position that it has while the pulling means is acting on the stressing bar 33 will cause the coupling member 92 and the stressing bar 33 connected therewith to move slightly to the left of the position shown in FIG. 21. However, since the concrete of the slab 93 is set, the spacing members 59 will remain in their position in the concrete body, and upon release of the pulling means at the left hand margin of the slab 93, the stressing member 33 and the coupling member 92 shown in FIG. 21 Will have a tendency to return to the position these parts had prior to stressing of the tendon 78". Also, due to the compression exerted on the concrete body 93 by the bearing member 32 at the left end of the tendon 78 after after the tendon 78" has been stressed, the entire concrete body 93 will be put under compression, thus causing the slab 93 to be pressed toward the slab 94 to provide a tight joint at 98. Any tendency of the coupling member 92 to interfere with this action because of the movement thereof lagging behind that of the surrounding concrete is eliminated by the provision of the compressible sheath 99, which will yield sufficiently to permit any relative movement between the concrete body and the coupling member that may be necessary to assure the pressing of the slab 93 against the slab 94 in the manner above described, the provision of the sheath 99 being an improvement over the structure disclosed in my co-pending application Serial No. 409,622, now Patent No. 3,263,384, which is a division of my application Serial No. 3,851.

The actual movement of the parts to bring about the pressing of the marginal edge of the slab 93 against the marginal edge of the slab 94 sufficiently to avoid any open cracks between the two slabs, is very small. AlsO, in describing the action of the tendons 78 and 78" and the procedure carried out to obtain the closing of the joint at 95, While described in connection with a single tendon 78 and 78", in practice, would involve the stressing of all the tendons 78 in the slab 94 in the manner described for the single tendon and thereafter coupling all of the tendons 78" in the manner above referred to in position in the form for the slab 93, and after pouring the slab, stressing all of the tendons 78" in said slab 93, after the concrete has set in a similar manner as described for the single tendon hereinbefore.

In FIGS. 22 and 23 a cylindrical body, such as a tank, is shown, that is provided with a pair of sections 102 and 103 of an arcuate character, which are provided with joints at 104 and 105. While the cylindrical or circular in cross section structure is shown as being made up in two halves, the same principles could be applied to a circular concrete structure having a large number of sections. The section 102 is provided with pilasters 106 and 107 and the section 103 with pilasters 10S and 109. In order to prestress the concrete structure shown in FIG. 22, the tendons 110 are provided in each of the two sections of the structure, said tendons being of the same type as shown in FIG. 1, having the stressing members 33 at each end thereof and the spacing members 59 between the bearing plates 32 mounted in the pilaster and the stressing member, the structure being shown in the position of the parts after the tendons have been stressed. Each of said tendons is provided with high tensile strength Wire tension members 30, which are of the same character as the previously described high tensile strength wire tension members 30, and the tendons are arranged in such a position that the transverse rows of said tension members 30 in the tendons extend vertically, which will place all of the tension members 30 at the same radial spacing from the axial center of the cylindrical structure, and thus when said tendons are stressed the same stress will be put on each of the tension members 30'.

In order to apply pressure of the marginal edge of the slab 102 against the marginal edge of the slab 103 at the joint 104 and pressure of the marginal edge of the slab 103 against the marginal edge of the slab 102 at the joint 105 in the manner above described in connection with the slabs 93 and 94, the tendons 111 and 112 are provided. The tendons 111 have the tensions members 30' arranged therein, in the same manner as the tendons 110, and are provided with stressing members 33 at each end thereof, but spaced from hearing plates 32 only at the pilaster ends thereof by means of spacing members 59. The stressing members 33 at the end of tendons 111 lo cated at the joints 104 and 105 are not provided with bearing plates 32 or spacing members 59, since they are coupled during construction and prior to stressing to coupling members 92 of tendons 112. The tendons 112 are similarly provided with the high tensile strength wire tension members 30' that are connected with the coupling members 92 at one end thereof and have the stressing members 33 and bearing members 32 at the other ends thereof spaced from each other by the spacing members 59. It is to be noted that the members 33 are coupled to the members 92 at the joints 104 and 105 and that said members 33 and 92 are surrounded by the compressible sheaths 99. Normally the joints 104 and 105 will be placed approximately equidistantly from the pilasters thus providing equal elongation of the tendons 111 and 112.

After the tendons have been stressed by pulling on the members 33 secured thereto jointly at the pilasters 106 and 107 and placing the spacing members or shims 59 in position to retain the elongation of the tendons 110, the tendons 110 extending between the pilasters 103 and 109 are similarly stressed, thus placing the wall portions between the pilasters 106 and 107 and between the pilasters 108 and 109 under compression. By similarly exerting a pull on the stressing members 33 of the tendons 111 and 112 jointly, the Wall portions between the pilasters 106 and 108 and between the pilasters 107 and 109 will be put under compression, which will also put compression on the joints 104 and 105. No resistance to this joint compression is offered by the members 33 and 92 at the joints, since they are surrounded by the compressible sheath 99.

What is claimed is:

1. A tendon for prestressing reinforced concrete structures by a post-tensioning method, said tendon having a flat main body portion of greater width than thickness and comprising a plurality of high tensile strength steel wires extending longitudinally of said tendon and means for holding said wires in a single row transversely of said tendon with the laterally adjacent wires in said row in side by side contact, said holding means engaging said wires at longitudinally spaced intervals along said tendon and each comprising a pair of spring clips frictionally gripping said wires for sliding movement of said Wires lengthwise of themselves through said clips.

2. A tendon such as claimed in claim 1 in which each of said clips has a flat main body portion and hook ends, the flat main body portion of one of said clips of each pair extending across said row of Wires in engagement with a plurality of said wires on one side of said wires, the fiat main body portion of the other clip of said pair extending across said row of wires in engagement with a plurality of said wires on the opposite side of said wires and said hook ends of both of said clips having curved portions embracing the end wires of the row and each terminating in a retaining member extending on the opposite side of said Wires from the flat main body portion of said clip.

3. A tendon such as claimed in claim 1 in which each of said clips has a flat main body portion and hook ends, the fiat main body portion of one of said clips of each pair extending across said row of wires in engagement with a plurality of said wires on one side of said Wires, the flat main body portion of the other clip of said pair extending across said row of wires in engagement with a plurality of said wires on the opposite side of said wires and said hook ends of both of said clips having curved portions embracing the end wires of the row, said pair of clips being mounted on said Wires in side by side adjacency lengthwise of said wires.

4. The combination with a tendon for prestressing reinforced concrete structures comprising a plurality of high tensile strength steel wires, heads on said wires, a bearing member having openings therethrough through which said wires extend, and an elongated stressing bar having a longitudinally extending row of openings therethrough of smaller diameter than said heads, said heads being positioned on the side of said stressing bar remote from said bearing member, of a retainer bar extending lengthwise of said stressing bar for holding said heads in engagement with said stressing bar and said stressing bar in engagement with said bearing member, said retainer bar being U-shaped in cross section, having a transverse portion engaging said heads and legs extending on the opposite sides of said stressing bar and screw-threaded headed members extending through said transverse portion of said retainer bar adjacent opposite ends thereof and detachably connecting said retainer bar with said bearing member.

5. The combination with a tendon for prestressing reinforced concrete structures comprising a plurality of high tensile strength steel wires, heads on said Wires, a bearing member having openings therethrough through which said wires extend, an elongated anchor bar having a longitudinally extending row of openings therethrough of smaller diameter than said heads, said heads being positioned on the side of said anchor bar remote from said bearing member, and a retainer bar for holding said heads in engagement with said anchor bar and said anchor bar in engagement with said bearing member, said retainer bar being U-shaped in cross section, having a transverse portion, and legs engaging the opposite sides of said anchor bar, Welds connecting said legs of said retainer bar with said anchor bar and Welds connecting said anchor bar with said bearing member to secure said retainer bar against movement relative to said bearing member and clamp said heads between said anchor bar and retainer bar.

6. The combination with a rigid elongated stressing bar having undercut longitudinally extending shoulders thereon of a rigid pulling member having a pair of jaws provided with inturned flanges having undercut shoulders thereon complemental to the shoulders on said bar and engaging therewith and means for mounting said jaws to swing toward and away from each other about axes parallel to the undercut shoulders on said jaws.

7. In a post-tensioned concrete structure a bearing member mounted in a marginal portion thereof, a rigid elongated stressing bar mounted in spaced relation to said bearing member, said stressing bar having undercut longitudinally extending shoulders thereon, said bearing member and bar having aligning openings therein, tensioning members extending through said openings and having heads larger than said openings in said bar engaging the side of said bar remote from said bearing member, a second concrete structure adjacent said first concrete structure, a rigid elongated coupling member longitudinally slidably engaged with said bar having a transverse portion and legs having inwardly directed flanges thereon provided with undercut longitudinally extending shoulders engaging the undercut shoulders of said bar, said coupling member having a longitudinally extending row of openings in said transverse portion, tension members extending through said openings and having heads engaging the inner face of said transverse portion, a yieldable sheath of compressible material extending around the peripheral surface of said coupling member, and anchoring means at the remote portion of said second structure for holding said last mentioned tension members under tension.

References Cited by the Examiner UNITED STATES PATENTS 756,309 4/1904 Wight 52-690 778,416 12/1904 Kyle 52-223 977,345 11/1910 Tidnam et a1. 25-118 1,233,933 7/1917 Swartsfager 24-123.1 1,304,815 5/1919 Sharp 52-677 2,645,090 7/1953 Kinneman et al. 52-223 2,657,084 10/1953 Wiberg 24-2013 2,728,978 1/1956 Birkenmaier et al. 29-452 2,739,361 3/1956 Elsner 287-205 2,867,884 1/1959 Brandt 25-118 2,871,554 2/1959 Siegfried 29-452 2,927,452 3/1960 Heidenstam 52-224 2,941,394 6/1960 Brandt 52-223 2,950,575 8/1960 Rubenstein 52-221 2,963,273 12/1960 Lane 52-223 2,963,764 12/1960 Finsterwalder 52 223 3,022,713 2/1962 Friberg 52-230 3,036,356 5/1962 Greulich 52-223 3,038,225 6/1962 Ausnit 24-2013 3,060,639 10/1962 Fields et a1. 52-223 3,089,215 5/1963 Stubbs 52-223 FOREIGN PATENTS 155,756 3/1954 Australia.

489,515 1/1953 Canada.

345,491 10/1904 France. 1,032,214 3/1953 France.

643,988 10/ 1950 Great Britain.

694,596 7/1953 Great Britain.

FRANK L. ABBOTT, Primary Examiner.

JACOB L. NACKENOFF, HENRY SUTHERLAND, Examiners. J. L. RIDGILL, Assistant Examiner. 

7. IN A POST-TENSIONED CONCRETE STRUCTURE A BEARING MEMBER MOUNTED IN A MARGINAL PORTION THEREOF, A RIGID ELONGATED STRESSING BAR MOUNTED IN SPACED RELATION TO SAID BEARING MEMBER, SAID STRESSING BAR HAVING UNDERCUT LONGITUDINALLY EXTENDING SHOULDERS THEREON, SAID BEARING MEMBER AND BAR HAVING ALIGNING OPENINGS THEREIN, TENSIONING MEMBERS EXTENDING THROUGH SAID OPENINGS AND HAVING HEADS LARGER THAN SAID OPENINGS IN SAID BAR ENGAGING THE SIDE OF SAID BAR REMOTE FROM SAID BEARING MEMBER, A SECOND CONCRETE STRUCTURE ADJACENT SAID FIRST CONCRETE STRUCTURE, A RIGID ELONGATED COUPLING MEMBER LONGITUDINALLY SLIDABLY ENGAGED WITH SAID BAR HAVING A TRANSVERSE PORTION AND LEGS HAVING INWARDLY DIRECTED FLANGES THEREON PROVIDED WITH UNDERCUT LONGITUDINALLY EXTENDING SHOULDERS ENGAGING THE UNDERCUT SHOULDERS OF SAID BAR, SAID COUPLING MEMBER HAVING A LONGITUDINALLY EXTENDING ROW OF OPENINGS IN SAID TRANSVERSE PORTION, TENSION MEMBERS EXTENDING THROUGH SAID OPENINGS AND HAVING HEADS ENGAGING THE INNER FACE OF SAID TRANSVERSE PORTION, A YIELDABLY SHEATH OF COMPRESSIBLE MATERIAL EXTENDING AROUND THE PERIPHERAL SURFACE OF SAID COUPLING MEMBER, AND ANCHORING MEANS AT THE REMOTE PORTION OF SAID SECOND STRUCTURE FOR HOLDING SAID LAST MEMTIONED TENSION MEMBERS UNDER TENSION. 